Drive device, especially for moving and turning the slats of a blind in a runner

ABSTRACT

In a drive device which is especially suitable for moving and turning the slats of a blind in a runner and in which the rotational movement of a drive wheel ( 2 ) can be alternately transmitted to a turning drive means effecting the rotational movement of the slats and to a transport drive means effecting the movement of the salts in the runner, the drive wheel ( 2 ) is driven by electric motor and, in addition, the shift of the change gear from its one shifting position into the other shifting position is effected by an electrical signal. For this purpose, a toothed sleeve ( 3 ) driving the transport drive means and a toothed sleeve ( 4 ) driving the turning drive means is alternately coupled to a drive tube ( 1 ), which can be driven via the drive wheel ( 2 ), in dependence on the relative rotational position of a reversing shaft ( 10 ) in the drive tube ( 1 ) via locking members ( 7, 8 ) arranged on its periphery. A brake disk ( 24 ) of magnetizable material, which faces an electromagnet ( 25 ), is mounted on the reversing shaft ( 10 ). When the electromagnet ( 25 ) is not excited, the reversing shaft ( 10 ) is rotationally entrained by the drive tube ( 1 ) and when the electromagnet ( 25 ) is excited, the brake disk ( 24 ) is attracted, the reversing shaft ( 10 ) thus held in its position and the drive tube ( 1 ) can be rotated with respect to the reversing shaft ( 1 ) against a restoring force.

CROSS-REFERENCE TO RELATED ART. (NOT APPLICABLE) STATEMENT REGUARDINGFEDERALLY SPONSORED RESEARCH OR DEVELOPMENT. (NOT APPLICABLE) REFERENCETO A “MICROFICHE APPENDIX” (SEE 37 CFR 1.96). (NOT APPLICABLE)DESCRIPTION BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a drive device, especially for moving andturning the slats of a blind in a runner, wherein the rotationalmovement of a drive wheel can be alternately transmitted to a turningdrive means effecting the turning movement of the slats by means of achange gear and to a transport drive means effecting the movement of theslats in the runner, wherein the change gear comprises a drive tube,which can be driven in both directions of rotation via the drive wheel,and a shaped reversing shaft extending coaxially to the drive tube,which can be rotated by a certain angle relative to one another, andwherein the drive tube is connected to a drive for the transport drivemeans to rotate therewith via locking members arranged offset in thelongitudinal and peripheral direction over its periphery in dependenceon the angular position of the reversing shaft with respect to the drivetube in one shifting position and is connected to a drive for theturning drive means to rotate therewith in another shifting position.

2. Description of the Related Art Including Information Disclosed Under37 CFR 1.97 and 1.98.

Such a drive device is known from DE-A 2 223 610. In this arrangement, adrive wheel, which can be operated by a cord or chain pull, rotates adrive tube with which it is engaged. In the wall of this drive tuberadially movable locking members are provided, offset with respect toone another both in the peripheral and in the longitudinal direction,which, depending on the position of a shaped shaft, which can also berotated by the drive wheel via a driving device within the drive tube,are held in engagement with one of two toothed sleeves arranged behindone another on the drive tube or can be moved out of the area ofengagement with the respective other toothed sleeve. A turning shafteffecting the turning of the slats can be driven via one of the twotoothed sleeves and a transport spindle effecting the movement of theslats can be driven via the other one. By changing the direction ofrotation at the drive wheel, the blind can thus be pulled open and shutby means of the longitudinal displacement of the slats, on the one hand,and, on the other hand, brought into a position allowing more or lesslight to pass in a state in which the blind is pulled shut wholly orpartially, that is into a wholly or only partially closing position, byturning or rotating the slats around their longitudinal axis.

Since the blind cannot be pulled open, i.e. the slats cannot be pushedtogether not, without interference when the slats are in theircompletely closing turning position because they then abut one another,a further development of the said gear ensures that each directionalchange at the drive wheel is followed by a turning or rotating of theslats and the turning shaft is decoupled at the gear and the drive isshifted to the transport spindle only after a certain angle of rotationhas been reached which goes beyond the closing of the slats.

Shifting from one shifting position to the other one is effected by alimited relative rotation between the drive tube and the shaped shaftand this relative rotation is made possible by a toothed disk which ispermanently joined to the shaped shaft and has mirror-inverted lockingteeth on both sides, with a driving and a sliding edge, which, on oneside, can lock in to a notched disk permanently joined to the drivewheel and, on the other side, into a second notched disk permanentlyjoined to the drive tube, wherein the drive tube, after the locking, isentrained by driving tabs which protrude into arc-shaped slots of thedrive wheel and allow a relative rotation of the drive wheel withrespect to the drive tube. The individual parts of the mechanicalshifting arrangement are exposed to high torques and surface pressuresduring the operation which can lead to premature wear and also todisturbances due to jamming. To ensure as trouble-free operation ofthese drive devices as possible, it is necessary to maintain very smallproduction tolerances in the parts of the mechanical shiftingarrangement, which makes production more expensive.

Moreover, it has been found in practical application that the shiftingprocess which is subdivided into a number of part-processes, and whichrequires a brief turning back and forward at the drive wheel with eachshifting process for example, is considered to be too complicated bymost users. Because of this complicated shifting process, this drivedevice is also not very suitable for an electric motor drive.

In DE 2 737 416 C2 and DE 25 54 991 B2, a gear is described in which theshaped shaft described above is held in a central rest position withrespect to the drive tube, or always returned to this position in whichthe locking members, which can be radially moved in the drive tube, areheld in engagement with the toothed sleeve via which the turning shaftis driven, by a restoring spring so that, when the drive wheel isturned, initially it is always the turning shaft which is first drivenand, as a consequence, the slats are rotated, i.e. turned, around theirlongitudinal axis. At the transport spindle, a free run, limited in bothdirections by a roller and by a stop, is provided which allows a nexttoothed sleeve meshing with the second tooth sleeve driven by the drivetube to rotate loosely on the transport spindle up to the end of thefree run. At the end of the free run, a non-positive connection isobtained between the transport spindle and the toothed sleeve whichrotates loosely on the former up until then, so that the transportspindle is now entrained in the rotation. Due to the higher torque to betransmitted by the drive tube during this process, the shaped shaft ispivoted against the force of the restoring spring inside the drive tubeand relative to the latter by a driving device, to such an extent that,as a result, the toothed sleeve driving the turning shaft is decoupled.

The transport spindle which is now coupled on alone effects the movementof the slats in the runner. The angle at which the slats are positionedwith respect to the running direction here always corresponds to one ofthe end turning positions of the slats and is determined by the lengthof the free run; it is approx. 150° in both directions. To ensure theshifting from turning to moving, a braking device which can be adjustedby means of an adjusting screw is also provided on the free-run shaft,by means of which the higher torque required for the shifting can beincreased again.

While the drive wheel can also be driven by electric motor instead ofwith the aid of a cord or chain pull in this case, the shifting fromdrive to the turning shaft to drive to the transport spindle is donepurely mechanically. Because of the large torques occurring during thisprocess, individual parts, especially of the limited free run in its endpositions, are subject to high loading. The forces and surface pressureoccurring during this process can lead to wear and also to jamming as aconsequence of production tolerances. In addition, it is no longerpossible subsequently to change or adapt the number of idle rotationsbetween the toothed sleeve and the transport spindle driven by it.

It has also been found that, in spite of the angular position of theslats of 150° with respect to the running direction during the movementof the slats, the latter tend to become hooked together, especially ifthey are loosely connected to one another by beaded strings at theirfreely suspended ends or if the runner is attached to an inclinedsurface, for example a roof slope. The slats also require a relativelylarge amount of space on the side, e.g. of a window, in thepushed-together state, that is to say when the blind is open, with anangular position of approx. 150°.

BRIEF SUMMARY OF THE INVENTION

It is the object of the invention to create a drive device of the typeinitially mentioned, the change gear of which is suitable for anelectric motor drive and in which too high a load on individual parts ofthe change gear, and this their premature wear, is avoided. Fewerindividual parts which have to be manufactured with high precisionshould be required and thus the production costs lowered. It should bepossible for the slats of a blind to move in a trouble-free manner,especially without becoming hooked into each other and impeding oneanother, along the runner for pulling the blind open and shut and, inaddition, to rotate them continuously in both directions between awholly and an only partially closing rotating or turning position ineach position of movement of the slats in order to regulate by thismeans the incidence of light. The shifting process from turning tomoving and conversely should be simplified in such a manner that it,too, and not only the movement itself, can be effected by electrical orelectronic means so that the device also becomes bus-capable for thecentral operation and control of a number of blinds individually or ingroups. Trouble-free operation should be guaranteed.

According to the invention, this is achieved by the fact that thereversing shaft is connected to a magnetizable brake disk which faces astationary electromagnet to rotate therewith and that when current flowsthrough the induction coil of the electromagnet, the brake disk ispulled against the electromagnet 25 and thus the reversing shaft isstopped against rotation and the drive tube can be rotated by an anglecorresponding to the two shifting positions relative to the reversingshaft whilst when the induction coil of the electromagnet is withoutcurrent, the reversing shaft and brake disk can be rotated together withthe drive tube.

In this manner, the shifting process based on a relative rotationbetween drive tube and reversing shaft can be carried out by anelectrical signal. The shifting process puts much less load on theindividual mechanical parts than in known devices so that premature wearand also operational disturbances, e.g. due to jamming are avoided. Theslats of the blind can also be rotated about their longitudinal axis inany intermediate moving position and not only, as known, when the blindis completely closed, and thus the incidence of light can be regulated.The drive device is distinguished by a compact space-saving type ofconstruction and the production costs are considerably reduced.

In accordance with a preferred embodiment, the drive tube and thereversing shaft and brake disk are held in a center positioncorresponding to one shifting position of the change gear with respectto one another by the force of a restoring spring where the inductioncoil of the electromagnet is without current, and can be jointlyrotated, but when current flows through the induction coil of theelectromagnet, the drive tube is rotated by the angle corresponding tothe other shifting position relative to the reversing shaft against theforce of the restoring spring. The change gear of the drive deviceaccording to the invention can thus be advantageously shifted in bothdirections.

As an alternative, the drive tube and the reversing shaft can be held inthe one shifting position with respect to one another, in which they canbe jointly rotated, when current flows through the induction coil of theelectromagnet; when the induction coil of the electromagnet is withoutcurrent, the drive tube can then be rotated by an angle corresponding tothe other shifting position of the change gear with respect to thereversing shaft by means of a braking force, e.g. of a brake spring.

The exciter current for the electromagnet is preferably switched on andoff in dependence on the angular position of the slats of the blind withrespect to the direction of movement. It is then possible to avoid theslats becoming hooked together or otherwise impedeing one another bybringing the slats into a certain angular position, preferably 90° withrespect to the direction of movement before they are moved.

The exciter current for the electromagnet can be switched on and off bymeans of an electronic circuit in dependence on time or analog values ornumber of pulses.

According to a preferred embodiment of the invention, when the drivedevice is operated the position of movement of the slats in the runnerand their angular position with respect to the direction of movement canbe electronically detected and the exciter circuit for the electromagnetcan be closed or interrupted in dependence on these two positions of theslats.

The change gear can preferably be held in the shifting position drivingthe transport drive means only at a defined angular position of theslats of approx. 90° with respect to the direction of movement, orbrought into this shifting position. In this angular position of theslats, they cannot impede each other during the movement in the runner,especially also on a slope.

In the case of an angular position of the slats deviating from approx.90° with respect to the direction of movement, first the change gear isbrought into the shifting position driving the turning drive means whenthe drive device is operated.

It is only in the end position of movement of the slats, whichcorresponds to the completely opened blind, that the change gear cannotbe brought into the shifting position driving the turning drive meansbecause in this case they are automatically located in the correct andalso space-saving angular position of approx. 90° with respect to thedirection of movement for a movement in the reverse direction at the endof a preceding moving process; this ensures that the slats, on the onehand, can be rotated, that is to say turned, about their axis, both withthe blind pulled shut and also in any intermediate position of movement,for regulating the incidence of light, and, on the other hand, with theblind completely opened when the slats are hanging closely next to oneanother in the angular position of 90°, their rotation and thusinterference can be avoided.

Since the moving of the slats normally requires a longer period of timethan the turning, it is considered to be advantageous if, where theinduction coil of the electromagnet is without current, the shiftingposition assumed by the change gear is the one in which the transportdrive means for moving the slats in the runner can be driven, and theshifting position assumed by the change gear when current flows throughthe induction coil of the electromagnet is the one in which the turningdrive means for rotating or, respectively, turning the slats can bedriven.

Due to the fact that the circuit of the change gear is electronicallycontrolled, together with the electric motor drive of the drive device,the latter is also provided with bus capability. A number of motors,that is to say a number of blinds, can be operated and controlledcentrally via a bus system individually or in groups.

The device is preferably driven with the aid of synchronous motors;these have the advantage that, in contrast to, for example, DC motors,they always run evenly. This attains special significance in the case ofblinds, the slats of which are carried in a runner at both ends. Such atwo-sided guidance can be of advantage, for example in the case of verylong slats and/or very windy installations or could also be required,for example, in the case of roof windows or in the case of horizontallyarranged slats.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

In the text which follows, the invention will be described in greaterdetail by way of example in a preferred embodiment with reference to theappended drawings, in which:

FIG. 1 shows a longitudinal section through a preferred embodiment of achange gear for a drive device according to the invention in oneshifting position,

FIG. 2 shows a cross section through the change gear according to FIG. 1along section line II—II in FIG. 1,

FIG. 3 shows a longitudinal section through the change gear according toFIG. 1 in its second shifting position,

FIG. 4 shows a cross section through the change gear along section lineIV—IV in FIG. 3,

FIG. 5 shows a cross section through the change gear along section lineV—V in FIG. 1, and

FIG. 6 shows a cross section through the change gear along section lineVI—VI in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

A drive tube 1 is subdivided by a gradation into a wider section 1 a anda narrower section 1 b. A drive wheel 2 constructed as toothed sleeve,which meshes with a toothed wheel, not shown, which can be driven by anelectric motor, preferably a synchronous motor, is pushed onto the widersection 1 a of the drive tube 1 and connected to the latter to rotatetherewith. A first 3 and second toothed sleeve 4 are arranged rotatablybut secured against longitudinal movement on the narrower section 1 b ofthe drive tube 1. In the area of coverage of the two toothed sleeves 3and 4, two, preferably three, groups of openings 5 and 6 are providedoffset with respect to one another in the peripheral direction and inthe longitudinal direction in the wall of the drive tube 1, in whichopenings locking members 7 and 8, preferably in the form of rollers, arearranged to be radially moveable and can be brought into or out ofengagement with driving noses 9 constructed on the inside wall of therespective tooth sleeve 3 and 4. As can also be seen from FIGS. 2 and 4,the radial movement of the locking members 7 and 8 in the openings 5 and6 is effected by a reversing shaft 10 which coaxially extends in thedrive tube 1 and which exhibits a triangular profile, at least in thenarrower section 1 b of the drive tube 1 in the embodiment shown,wherein the rounded corners of the triangle form projections 11 slidingalong the inside wall of the narrower section 1 b of the drive tube 1and the sides of the triangle form indentations 12 with respect to thewall of the drive tube 1 surrounding them. The drive tube 1 and thereversing shaft 10 can be rotated relative to one another. Depending onthe position of the reversing shaft 10 in the drive tube 1, the lockingmembers 7 or 8 are pushed radially outward by the projections 11 of thereversing shaft 10 in the area of coverage of one of the two toothedsleeves 3 or 4 and are brought or held in engagement with the drivingnoses 9 of the relevant toothed sleeve 3 or 4 so that a rotationallyfixed connection is established (see FIG. 4) whilst the locking members8 or 7, which are offset in the peripheral direction, can escape intothe indentations 12 of the reversing shaft 10 in the area of coverage ofthe other toothed sleeve 4 or 3 and thus this toothed sleeved 4 or 3 isdecoupled from the drive tube 1, the drive tube 1 can therefore rotatefreely within this decoupled toothed sleeve 4 or 3 (see FIG. 2). Aturning drive means, e.g. a turning shaft, for rotating the blind slatscan be driven via one of the two toothed sleeves 3 and 4 in a mannerknown per se, whilst a transport drive means, e.g. a transport spindle,for moving the blind slats can be driven via the other toothed sleeve 4or 3. In the text which follows, it will be assumed that a transportspindle can be driven via the toothed sleeve 3 in the shifting positionshown in FIG. 1 whilst a turning shaft is driven via the toothed sleeve4 in the other shifting position according to FIG. 3.

On the part of the reversing shaft 10 protruding through the widersection 1 a of the drive tube 1, a round cam disk 13 is arranged torotate therewith. A circular sector-shaped recess 14 on the periphery ofthis cam disk 13 forms two stops 15 and 16 (see FIGS., 5 and 6). In thecenter between these two stops 15 and 16, an axial extension 17 ismolded onto the cam disk 13. A restoring spring 18 placed in a spiralonce or several times loosely around the reversing shaft 10 engages withits two leg ends 19 and 20 crossed-over, on the one hand, on theextension 17 of the cam disk 13 and, on the other hand, on a stud 22protruding from the drive tube 1 or a molded part 21 permanentlyconnected to the latter. The reversing shaft 10 is thus held in acentral position with respect to the drive tube 1, in which position, aswill still be explained below, preferably the toothed sleeve 3, viawhich the transport spindle is driven for moving the slats, is alwayscoupled to the drive tube 1 whilst the toothed sleeve 4 driving theturning shaft can be loosely rotated with respect to the drive tube 1(see FIG. 1). An axial projection 23 which, together with the cam disk13, forms a hollow space for the partial accommodation and for theprotection of the restoring spring 18 can be provided on the cam disk 13diagonally opposite the recess 14.

On the section of the reversing shaft 10 protruding from the widersection 1 a of the drive tube 1, a brake disk 24 of magnetizablematerial is arranged to rotate therewith and, following the brake disk,leaving an airgap, an electromagnet 25 is arranged in a stationarymanner, in which the reversing shaft 10 is rotatably supported and whichcan be excited and deexcited controlled by electronics. When theinduction coil of the electromagnet 25 is without current, the reversingshaft 10 is held in its central position by the restoring spring 18 withrespect to the drive tube 1, i.e. when the drive tube 1 is driven in onedirection via the drive wheel 2 by an electric motor, the reversingshaft 10 and cam disk 13 and brake disk 24 are entrained in thisrotation by the force of the restoring spring 18 and the change gearremains in the shifting position assumed, in which the transport spindleof the blind is preferably driven via the toothed sleeve 3 which isconnected to the drive tube 1 to rotate therewith (see FIGS. 1 and 5).

If current is fed to the induction coil of the electromagnet 25, theelectromagnet field being built up attracts the brake disk 24 to theelectromagnet 25 and thus the reversing shaft 10 and cam disk 13 arealso held in their position. The drive tube 1 which is now drivenfurther via the drive wheel 2 rotates with respect to the reversingshaft 10 against the force of the restoring spring 18 until the stud 22,permanently connected to it, abuts against one of the two stops 15 or 16of the cam disk 13 (see FIG. 6). In this relative movement between drivetube 1 and reversing shaft 10, the change gear assumes its othershifting position in which the projections 11 of the reversing shaft 10move the locking members 8 radially outward in the openings 6 of thedrive tube 1 and into the range of movement of the driving noses 9 ofthe toothed sleeve 4 driving the turning shaft, the latter thus beingcoupled to the drive tube 1, and in which the locking members 7 canescape into the indentations 12 of the reversing shaft 10 in theopenings 5 of the drive tube 1 which are offset in the peripheral andlongitudinal direction, so that the toothed sleeve 3 driving thetransport spindle is decoupled from the drive tube 1 (FIGS. 3 and 4).

If the exciter current of the induction coil is interrupted, the brakedisk 24 is no longer kept attracted to the electromagnet 25. Therestoring spring 18 which has been deflected from its rest position andis correspondingly tensioned now attempts to restore the cam disk 13 andits associated reversing shaft 10 back to the central rest position withrespect to the drive tube 1 so that the change gear resumes its firstshifting position for moving the slats in their runner. Thus, shiftingof the transport spindle to the turning shaft and conversely is effectedby an electrical command from an electronic control.

Since the turning of the slats is the shorter process in terms of timein comparison with their movement in the runner, it is preferred, asdescribed, to allow the change gear to assume the shifting positioneffecting the turning of the slats when current flows through theinduction coil of the electromagnet 25 whilst the moving of the slats iseffected where no current flows through the induction coil; inprinciple, however, it is also possible to reverse the procedure.

So that the slats cannot become hooked together or otherwise impede oneanother in any way when they are moved in the runner, the slats aremoved at an angular position of the slats with respect to the directionof movement which is predetermined by the electronics, advantageously atan angular position of about 90° to be specific. If, accordingly, theslats are always at right angles to the direction of movement during themovement, they cannot only not impede one another but the additionaladvantage is obtained that they take up less space in the completelypushed-together state, that is to say when the blind is completelyopened, on the side, for example of a window, than if they are atanother angle, and they can there be covered by a relatively narrowpanel which is frequently desirable for esthetic reasons.

When the drive device is operated, both the position of movement and theturning position of the slats can be advantageously detected by suitableprobes, e.g. by a light barrier and/or a hall element by the electronicscontrolling, e.g. opening and closing, the exciter circuit of theelectromagnet 25, and the exciter circuit of the electromagnet 25 can becontrolled in dependence on these positions.

Assuming the slats are in their position where they are completelypushed together on one side of the runner and are thus mandatorily inthe angular position of approx. 90° to the direction of movement whichis preferred for the movement, the electromagnet is not excited when thedrive device is operated since it is not necessary to rotate the slatsfor the subsequent movement closing the blind.

If the slats are in their other end position of movement or in anintermediate position when the drive device is operated, first theelectromagnet 25 is excited and accordingly the change gear is broughtinto its position driving the turning shaft. The slats are then rotatedabout their axis, controlled for example by time or by analog values ornumber of pulses, until either the desired incidence of light throughthe blind or again the angular position of approx. 90° to the directionof movement is achieved in order to be able to initiate a new movingprocess. The electronics can detect from the duration of operation ofthe drive device by an operator at an operating switch whether it isonly desired to turn the slats for regulating the incidence of light orturning with subsequent movement of the slats.

As already mentioned, each of the devices is preferably driven by asynchronous motor. These have the advantage that, in contrast to, forexample, DC motors, they always run evenly. This is of particularsignificance if the slats of the blind are guided and driven in a runnerat both ends. It can be seen quite easily that in such a blind,trouble-free operation is only possible when the drive motors on bothsides of the slats run absolutely uniformly. Guiding the slats on bothsides is especially advantageous in the case of relatively long slats orin very windy installations; they are even required on roof windows orin the case of horizontally arranged slats.

LIST OF REFERENCE DESIGNATIONS:

1 Drive tube

1 a Wider section

1 b Narrower section

2 Drive wheel

3 First toothed sleeve

4 Second toothed sleeve

5,6 Openings

7,8 Locking members

9 Driving noses

10 Reversing shaft

11 Projections

12 Indentations

13 Cam disk

14 Recess

15,16 Stops

17 Extension

18 Restoring spring

19,20 Leg ends Molded part

22 Stud

23 Projection

24 Brake disk

25 Electromagnet

What is claimed is:
 1. A drive device, especially for moving and turningthe slats of a blind in a runner, wherein the rotational movement of adrive wheel (2) can be alternately transmitted to a turning drive meanseffecting the turning movement of the slats by means of a change gearand to a transport drive means effecting the movement of the slats inthe runner, wherein the change gear comprises a drive tube (1), whichcan be driven in both directions of rotation via the drive wheel (2),and a shaped reversing shaft (10) extending coaxially to the drive tube(1), which can be rotated by a certain angle relative to one another,and wherein the drive tube (1) is connected to a drive for the transportdrive means to rotate therewith via locking members (7, 8) arrangedoffset in the longitudinal and peripheral direction over its peripheryin dependence on the angular position of the reversing shaft (10) withrespect to the drive tube (1) in one shifting position and is connectedto a drive for the turning drive means to rotate therewith in anothershifting position, characterized in that the reversing shaft (10) isconnected to a magnetizable brake disk (24), which faces a stationaryelectromagnet, to rotate therewith and that when current flows throughthe induction coil of the electromagnet (25), the brake disk (24) ispulled against the electromagnet (25) and thus the reversing shaft isstopped against rotation and the drive tube (1) can be rotated by anangle corresponding to the two shifting positions relative to thereversing shaft (10) whilst when the induction coil of the electromagnet(25) is without current, the reversing shaft (10) and brake disk (24)can be rotated together with the drive tube (1).
 2. The drive deviceaccording to claim 1, characterized in that the drive tube (1) and thereversing shaft (10) and brake disk (24) are held in a center positioncorresponding to one shifting position of the change gear with respectto one another by the force of a restoring spring (18) where theinduction coil of the electromagnet (25) is without current, and can bejointly rotated, but when current flows through the induction coil ofthe electromagnet (25), the drive tube (1) can be rotated by the anglecorresponding to the other shifting position relative to the reversingshaft (10) against the force of the restoring spring (18).
 3. The drivedevice according to claim 1 or 2, characterized in that the excitercurrent for the electromagnet (25) can be switched on and off independence on the angular position of the slats of the blind withrespect to the direction of movement.
 4. The drive device according togroups claim 3, characterized in that the exciter current for theelectromagnet (25) can be switched on and off by means of an electroniccircuit in dependence on time or analog values or number of pulses. 5.The drive device according to claim 3, characterized in that when thedrive device is operated, the position of movement of the slats in therunner and their angular position with respect to the direction ofmovement can be electronically detected and the exciter circuit for theelectromagnet (25) can be closed or interrupted in dependence on thesetwo positions of the slats.
 6. The drive device according to claim 5,characterized in that the change gear can be held in the shiftingposition driving the transport drive means, or can be brought into thisshifting position, only at a defined angular position of the slats ofapprox. 90° with respect to the direction of movement.
 7. The drivedevice according to one of claims 1 to 6, characterized in that theshifting position assumed by the change gear where the induction coil ofthe electromagnet (25) is without current is the one in which thetransport drive means for moving the slats in the runner can be driven,and the shifting position assumed by the change gear when current flowsthrough the induction coil of the electromagnet (25) is the one in whichthe turning drive means for rotating or turning the slats about theirown axis can be driven.
 8. The drive device according to one of thepreceding claims, characterized in that the slats of a blind are guidedin a runner at both their ends and drive is in each case effected by asynchronous motor via a drive device according to the invention.